The present invention is related to a low brake pipe pressure detecting circuit for assuring that a brake application is initiated on a railway train in the event the train brake pipe pressure drops below a predetermined safe operating value and, more particularly, to a manner of automatically resetting the circuit.
Pilot-operated vent valve devices, such as those employed in the standard 26-B type locomotive brake valve, manufactured by the Westinghouse Air Brake Company, typically employ a poppet-type disc valve carried by a stepped differential piston subject on one side to a pilot pressure that acts over a substantially larger area than the opposing area of the stepped piston subject to brake pipe pressure and main reservoir pressure to normally maintain the valve seated and thereby prevent the brake pipe pressure from being exhausted to atmosphere. When the pilot pressure is exhausted, the force exerted by the brake pipe pressure and main reservoir pressure is effective to unseat the valve, whereby brake pipe pressure is vented to atmosphere and an emergency brake application is obtained in a well-known manner. Various penalty brake arrangements, such as safety or "deadman" control, train control and overspeed control, are predicated on the basis of such a vent valve configuration, whether incorporated in a brake valve device, such as the above-mentioned 26-B type, or a separately contained vent valve device. Actuation of any of the aforementioned systems will invoke a penalty brake application by causing an exhaust of the vent valve pilot pressure to actuate the vent valve device, which in turn exhausts the train brake pipe pressure to produce the desired penalty brake application.
Attempting to employ a vent valve device of the type described to initiate a train brake application whenever an undesirably low brake pipe pressure is detected, however, presents a problem as to how to reset the vent valve device so that brake pipe pressure can be recharged to release the brake application initiated by the low brake pipe pressure detecting circuit.
Such a reset function can be accomplished manually, but would impose another requirement on the operator, in addition to the normal brake valve manipulations he is already required to make.